What in the world is this? Why do i need to know about it? When do i need to reference it?
Update… thanks for the tips on kerf!
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There’s a TON of info here on kerf. Here’s a forum search to get you started: https://community.glowforge.com/search?q=kerf
EDIT: Sorry, meant to give you a little more than that! Kerf is the amount of material the laser vaporizes off the edge of your material. It matters if you’re trying to get things to fit tightly together, like when building boxes or doing inlays. Enjoy your trip down the rabbit hole!
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Thanks! I searched forum before posting. Yes, there are a ton of posts. However, i think that a basic introduction to kerf would help a lot of us newbies. Most of the posts are a little beyond that.
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Pretty sure there is one somewhere…try focusing your search on the “Glowforge tips and tricks” category; there should be some tutorials over there. 
I’ll go do some digging too, need to get dinner finished real quick first!
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Ahh, found it in the Matrix (linked in the top pinned post in “Glowforge Tips and Tricks,” for future reference). Click on “Designing for your Laser.” When the spreadsheet opens, scroll down to around Row 150, and there are links to kerf tutorials for various vector programs.
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Define kerf: The gap created by a cut.
Think of it this way: If you have a piece of wood that is 6" long and you take a saw and cut it in half, you don’t end up with two 3" pieces of wood. Instead, you have two pieces of wood that are slightly shorter than 3" and a bunch of sawdust. This is because the saw removed some of the wood.
The laser works the same way. It cuts the wood/acrylic in half, but it removes a tiny amount of material. Depending on the material, the kerf (gap created by the laser) can vary from 0.002" to 0.022". I know, these sound like really tiny fractions. However, you have a laser that is accurate to 0.001".
From my notes (https://hackerfactor.com/glowforge.php):
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On really hard material, just assume the kerf is 0.002" (0.05mm).
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In general, kerf on PG hardwood is about 0.002", and 0.002-0.022" in general.
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PG Medium Maple has a kerf around 0.008".
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PG Draftboard has a kerf around 0.002" (use 0.05mm - 0.06mm; 0.05 is barely loose; 0.055mm is good).
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PG Acrylic has a kerf around 0.002" (0.05mm).
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Zebrawood, Purpleheart, and other really hard woods have a kerf around 0.002" (0.05mm).
The place you will notice kerf:
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If you are cutting out something for a bezel, the kerf will be the difference between a snug fit and able to slide around without glue.
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If you are making finger joints, then not accounting for the kerf will result in a really loose fit. (You will need glue.) With just the right kerf, you can push the joint together and it will stay forever without glue. (I have some boxes I made with really right fits.) And if the correction for the kerf is too much (e.g., adding in 0.005 when you really needed 0.002), then have a small jewelry file or fine sandpaper handy and be ready to make the gap a little bigger.
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If you are doing an inlay, then kerf can be the difference between “fit”, “too loose”, and “don’t fit.”
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Dont’ worry about kerf if you’re doing an inlay into an engrave. Only worry about it if you’re trying to fit a cut with a different cut.
Hope this helps!
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Awesome!! Thank you so much for taking the time to write this up!! 
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We didn’t just make the word up, it’s in the dictionary:
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Thanks for that-
You are a saint @dr.krawetz.
@simplygage, it sure is a challenging concept to learn about. I appreciate your experience in searching the forum and still feeling like the answers aren’t there.
Would you do me a favor and read this post and then post here whatever questions or need for clarity? A lot of forum veterans have the idea that anything you need has been discussed and beaten like a dead horse enough to “feed France for a month.”
It might help us all figure out how to make these basic concepts more accessible to new users.
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This is the tricky part about the forum as it ages and gets more and more content. It can be hard to get a straight answer just by searching, so what’s a new user to do? Sometimes you just gotta ask.
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Easy way to see kerf in action: Cut a square in a piece of material on your laser. Reach in and feel how that piece jiggles inside the part that it was cut out of. That is kerf.
If you want to make another square that fits tightly in that first “hole”, you have to re-size the square a little larger than the hole, so once the laser burns the material off the edge of the square, its size closely matches the hole.
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Technically, that is 2x kerf. 
I make a lot of small boxes and I never use kerf adjust for any of them. If the joints were any tighter they would be hard to assemble. As is, they kind of snap together and a little glue ensures they won’t come apart. I recommend playing around without trying a kerf adjustment and see what you think.
examples:
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Ditto that here. Although recently making the Nespresso box (which I now have orders for!) I only adjusted one side of the cut for kerf as doing both would have made it way to tight to have the trees fit without breaking them and doing neither side made too loose with gaps.
As with anything - depends on what you’re making. 9 times out of 10 I wouldn’t adjust for kerf, just use thick gorilla super glue and it fills gaps. 
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I like the challenge of making boxes without glue. A gentle push and these snap together perfectly. You can drop them and they’ll stay together.
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When you get really anal about kerf allowance, you may also want to consider the taper (bevel) of the cut…
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One other thing to note about kerf is that when done with a well balanced saw, the two sides of the cut are perpendicular, aka straight. A laser beam is sorta hour glass shaped and leaves an angled edge. The thicker the material the more noticeable this is.
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Yep. And consider flipping inlays over to get the taper of the kerf to match perfectly.
I’m actually using the taper of the cut to make wedges for joining layers together
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Life.Saver.
Thank you!